In Windows XP, Vista, and 7, there are times when all the icons on the desktop revert to generic white icons, then slowly return to their normal appearances one by one. What is Windows doing that causes this, and why does it take so much longer to redraw the actual icons than it does to simply replace them with generic icons?
I’m not an expert in areas related to Windows Desktop, but as a programmer of the past millenium I would say that it is easier to move one image (already in memory) several times to your adapter’s memory than to do several disk reads and load the images from your hard disk buffer to screen memory. AFAICT Windows is doing “other things” while refreshing your Desktop.
Windows is rebuilding your icon cache. I’ve personally never seen it do this on its own, though. Usually its an explicit command.
But I can explain the process, and answer your other questions. The icon information is actually in each program’s file. You have a lot of applications on your desktop. In order to not have to go back and find the file for each one (And every other icon you see), Windows stores the icons in a special file. This file can become corrupted, and thus must be rebuilt. Windows deletes the file, and then goes and find the icon for every icon on the screen. It’s opening multiple files, so it takes a while, as komolono says.
While it is doing this, it replaces the icon with the default icon, which is always in memory. So it takes no time at all to call up. The icon files on the disk take a lot more time, as disk is slower than memory.